For many years people have been trying to create better autostereoscopic 3D displays, and this invention provides a further advance in this field. An autostereoscopic display is a display that gives stereoscopic depth without the user needing to wear glasses. This is accomplished by projecting a different image to each eye. An autostereoscopic 3D display (hereafter 3D display) can be realised by using parallax optic technology such as a parallax barrier or lenticular lenses.
The design and operation of parallax barrier technology for viewing 3D images is well described in a paper from the University of Tokushima Japan (“Optimum parameters and viewing areas of stereoscopic full colour LED display using parallax barrier”, Hirotsugu Yamamoto et al., IEICE trans electron, vol E83-c no 10 Oct. 2000).
FIGS. 1a and 1b shows the basic design and operation of parallax barrier technology for use in conjunction with an image display for creating a 3D display. The images for the left eye and right eye are interlaced on alternate columns of pixels of the image display. The slits in the parallax barrier allow the viewer to see only left image pixels from the position of their left eye and right image pixels from the position of their the right eye.
The same autostereoscopic 3D effect as shown in FIGS. 1a and 1b can be achieved by using lenticular lenses. Each lens is substantially equivalent to a parallax barrier slit. FIGS. 2a and 2b shows a conventional 3D system comprised of lenticular lenses and an image display.
The lenses image the appropriate pixels of the image display to the viewer's eyes. As shown in FIGS. 2a and 2b, light from the left image pixels is directed into the observer's left eye, and vice versa. The focal lengths of the lenses are typically designed to be approximately equal to the lens-pixel separation distance (i.e. the focal length of the lens is approximately at the plane of the pixels).
The lenticular lenses may also have a light blocking material positioned between the lenses, as described by U.S. Pat. No. 7,813,042B2. The light blocking material reduces light leakage from between the lenses and consequently improves the quality of the 3D image.
The technologies illustrated in FIGS. 1a and 1b and FIGS. 2a and 2b can be configured to provide a high quality 3D mode. However, many applications exist whereby a display is also required to operate in a high quality 2D mode. Using the technologies illustrated in FIGS. 1a to 2b would yield a 2D image with half the native resolution of the image display—this is highly undesirable. For the image display to show an image with 100% native resolution in the 2D mode, the parallax optics (parallax barrier or lenticular) must be switchable between a first mode that provides substantially no imaging function (2D mode) to a second mode of operation that provides an imaging function (3D mode).
An example of a switchable parallax barrier technology is disclosed in U.S. Pat. No. 7,813,042B2. However, switchable parallax barrier technology has the disadvantage that the parallax barrier absorbs light in the 3D mode, reducing transmission by ˜65%. This inefficient light usage is a major disadvantage since the 2D mode and 3D mode will have a significantly different brightness. Boosting the brightness of the 3D mode can be achieved at the expensive of increased power consumption, which is highly undesirable, especially for mobile products.
An example of a switchable lens technology, based upon a physical lens in contact with liquid crystal, is disclosed in the paper by Commander et al (EOS Topical Digest Meetings, Microlens Arrays, vol. 5 (1995), pp 72-76).
U.S. Pat. No. 6,069,650 discloses an image display used in conjunction with a switchable lens (physical lenses in contact with liquid crystal) to create a display system that is switchable between a 3D mode and a 2D mode. The advantage of this switchable lens system is that the 3D mode is approximately the same brightness as the 2D mode. A first disadvantage of this technology is that the switchable lenses are more complicated and expensive to manufacture than a switchable parallax barrier. A second disadvantage of this technology is the degradation of the 2D mode image quality. This image degradation occurs because the refractive index of the liquid crystal varies as function of temperature and wavelength in a manner that does not exactly match that of the lens material. Consequently, a residual lensing effect occurs that causes an observable brightness non-uniformity.
WO05101855A1 describes the use of electro-wetting lenses that can be used in conjunction with an image display to realise a 3D display that can be switched between a 2D mode and a 3D mode. The disadvantage of this system is that the manufacture of electro-wetting lenses is complicated and expensive.
A liquid crystal lens (LC lens) is a switchable lens that uses conventional liquid crystal display (LCD) manufacturing processes. 3D display systems that use LC lenses have been disclosed by US2007/0296911A1, U.S. Pat. No. 7,375,784 and “30.3 Autostereoscopic Partial 2-D/3-D Switchable Display” by Takagi et al (SID DIGEST 2010 pp 436). The LC lens technologies described above have the disadvantage that the 3D mode is not high quality because the metric of 3D crosstalk for LC lenses is inferior to that of switchable parallax barrier technologies.
An electrode structure to enable a first 3D mode via a LC GRIN lens in a first orientation and second 3D mode via a LCD GRIN lens in a second orientation, from a single LC layer whereby the first and second orientations are orthogonal is disclosed in US2008/0266387A1.
The use of LC lens is also proposed in US 2009/0244682, US 2010/0026920, GB 2455614, and US 2011/0032438. US 2011/0032438 proposes the provision of light blocking members at regions where discontinuities occur in the LC lens.